The present invention relates to optical apparatus and in particular but not exclusively to electronic apparatus adapted for insertion into confined spaces to obtain a television image of an inaccessible object.
Such apparatus are well-known and are used as endoscopes to examine internal surfaces of, for example, human bodies and as borescopes to examine mechanical components such as engines, aero engines, and aircraft.
Whilst generally satisfactory there are a number of difficulties in utilizing such known apparatus. In particular, it can be difficult to obtain an image of sufficient contrast and resolution and furthermore, particularly when being used in an unfamiliar environment, it is difficult to obtain from the image produced an indication of the size of the objects being viewed.
It is known from EP0084435 to improve the contrast and resolution of an optical apparatus by providing means for focusing the optical system of the apparatus in which an intense spot of light is projected onto an object and the focus is adjusted until a clear image of the spot is formed. A disadvantage of such apparatus is that in some applications a high intensity source cannot be used and also the technique is not readily adaptable for use in an electronic imaging apparatus.
It is also known to provide a laser scanning camera for remote inspection purposes in which a laser beam is projected onto an object field and scanned in raster fashion, the reflected beam being detected and used to form a television image. A disadvantage of such cameras is that their bulk inhibits use in confined spaces.
It is also known to use an electronic imaging apparatus to provide a television image in which a solid state detector such as a charge coupled device is mounted at the tip of an apparatus tube. A disadvantage of such apparatus is that they cannot be used in certain hazardous environments where the tip is to be exposed to high levels of radiation such as in the inspection of nuclear reactors.
Throughout the specification we will refer to "light", "optical" and like expressions. It will be understood, however, that the present invention is not restricted to electromagnetic radiation of visible wavelengths, but may apply to other wavelengths such as infra-red and ultraviolet. The term "lens" used in the specification should also be understood to encompass groups of lens elements where appropriate.